This may be a dumb question but I often wonder why sensor sizes still equate to film sizes and whether or not we might see sensors grow to 6 by 6 or even 6 by 7. On medium format they seem to be stuck on 6 by 4.5.

Well I'm sure the tech types here will know more than me, but I think you will find larger sensors cost dramatically more than smaller ones, hence why full frame on 35mm is still in the minority. And another reason is going to be lenses. On a full frame DSLR the image circle of the lens covers up to around 36mm size image, and if the sensor gets bigger the lens would have to cover a bigger area. The same thinking applies to Medium Format. Besides which, how much extra quality do we need (within a sensible price range). How many current 6x7 cameras are there around which could take a 6x7 back now. Which manufacturer is going to invest in a whole new camera and lens system for a tiny number of end users? Personally I think the direction is more likely to be small sensors with very much better performance.

This may be a dumb question but I often wonder why sensor sizes still equate to film sizes

Actually they don't, eg APS-C, M4/3 plus all the smaller sensored compacts.Where they do, it means you don't need to design new lens designs and can re-use existing designs.

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whether or not we might see sensors grow to 6 by 6 or even 6 by 7. On medium format they seem to be stuck on 6 by 4.5.

Rather unlikely. As the size of ICs increase manufacturing costs escalate hugely, then add that few people actually want bigger cameras, bigger lenses, so as volumes fall costs again increase.35mm Full frame appears to be a sweet spot, as sensors are affordable, cameras are of manageable size and quality is high enough for the vast majority of users.

For sensors to get bigger, there has to be the potential for a market which will pay for the development effort. My opinion is that the marketplace is happy enough with the products out there now, that the chances of further enlarged sensors is pretty slim in the next 5 years. FF sensor cameras are selling, but prices seem to be limiting how fast they are penetrating the market. Large numbers of photographers seem pretty happy with their aps, m4/3 sensors and the like. I don't see the functional need that would drive a new larger design. IMO

This may be a dumb question but I often wonder why sensor sizes still equate to film sizes and whether or not we might see sensors grow to 6 by 6 or even 6 by 7. On medium format they seem to be stuck on 6 by 4.5.